1. Field of the Invention
The present invention relates to adhesive compositions containing polychloroprene and the methods of preparing the polychloroprene and adhesive composition thereof.
2. Description of the Prior Art
Polychloroprene has been long used as an adhesive component. Adhesive and cement compositions comprising chloroprene polymer, metal oxide, modified phenolic resin and solvent, having high adhesive strength are well known. The cements are dispersions of insoluble components in a liquid phase which consists of the solvent and material soluble therein. In solvent cements containing chloroprene polymers, it is common practice to include the reaction products of certain basic metal oxides and heat reactive phenol formaldehyde resins. The reaction product forms a complex with the rosin acid resulting in a dispersion which upon standing stratifies into layers consisting of the complex of metal oxide, phenolic resin reaction product and rosin acid in the bottom phase and the chloroprene polymer in the top phase.
This stratification, often called "phasing", is inconvenient to the user because of the need to redisperse the stratified layer prior to use of the cement.
Phasing has been a problem for which numerous techniques for its elimination have been proposed, for example, U.S. Pat. No. 3,185,658 to Garrett, added an organic acid; U.S. Pat. No. 3,308,087 to Garrett used a carboxyl-containing chloroprene polymer; U.S. Pat. No. 3,318,834 to Tabibian added a polyisocyanate and U.S. Pat. No. 3,394,099 to Garrett used a high molecular weight phenol formaldehyde resin, free of low molecular weight components.
In 1969, U.S. Pat. No. 3,427,268 was issued to J. A. Fries which disclosed the preparation of contact cements which did not phase using chloroprene polymers containing no more than 2% rosin or rosin based derivaties, however the only examples were polymers from which the rosin acids had been extracted by a post-polymerization procedure.
Subsequent to the Fries patent, the primary art approach to overcoming polychloroprene phasing has been based on the same principle of limiting the amount of rosin acids, or removing them altogether.
However, when the rosin acids are reduced or removed from the polymerization system they must be replaced with another saponifiable organic acid or a surface active agent as disclosed, for example, in the following U.S. Pat. Nos.: 3,824,203, Tabibian, disclosed a quaternary system of (a) from 0.5 to 1.5% "disproportionated" rosin acid (b) from 1 to 2% of an unsaturated fatty acid (c) a standard amount of naphthalene sulfonate condensate, and (d) a methyl ester of wood rosin in the amount of 2 times (a)+(b). 3,872,043, Branlard et al, used (a) to 1.8 to 3% "disproportionated" rosin acid, (b) up to 1% fatty acid, and adds (c) to the polymerization system an amount of up to 2.5% rosin derivative tackifiers. 3,899,459, Branlard et al, uses up to 0.5% "disproportionated" rosin acid (b) up to 2.5% fatty acid (c) 3 to 6% dimerized (or polymerized) rosin acid or partially esterified rosin acids, most of which is added as a post-polymerization addition. 3,941,738, Denda et al, completely eliminated rosin acids and substituted salts of aliphatic substituted benzoic acid or certain nonionic polyoxyethylene ether or esters.
As the preceding patents indicate, wood rosin and its derivatives are the preferred components to the polymerization emulsification system because of the tack they impart to the polymer to be used as adhesives. Also, the worldwide polychloroprene industry has been established with a process which utilizes the rosin acids and inorganic base soap for the purpose of emulsification and processing.
Rosin acids may be modified to eliminate the conjugated unsaturation of abietic acid which is susceptible to oxidation. The three principal methods of modification and (1) dehydrogenation ("disproportionation"); (2) hydrogenation; and (3) dimerization or polymerization.
It should be noted that while unmodified rosin is included in the discussion of the above patents, unmodified wood rosin is never included in any of the examples.
It is an advantage of the present invention that standard and conventional recipes for preparing chloroprene polymers with rosin may be used for preparing polychloroprene for use in adhesives. It is a further feature of the present invention that stabilizing additives are not necessary nor required to prevent phasing of the solvent, modified phenolic resin, chloroprene cements. These and other advantages and features will be apparent from the following discussion.